(1) Field of Invention
The present invention is directed to a system for generating a large pressure on a microfluidic chip and, more specifically, to a method and apparatus for generating pressure to drive and actuate microfluidic valves, pumps and other on-chip processes.
(2) Background
Recent developments in microfluidic technologies have enabled a variety of high-throughput biological assays to be performed on the surface of lab-on-chip devices. Microfluidic devices have characteristically small diameter channels and components, typically on the order of 100 micrometers (μm).
Suitable means to control and drive all the components for lab-on-chip applications are limited due to the size constraints of the field.
Common approaches for controlling flow throughout the lab-on-chips rely on the use of large external pressure sources, such as nitrogen bottles, to supply the pressure necessary to drive lab-on-chip operations. However, the very size of these external pressure sources greatly limits the portability of the lab-on-chip. Further, such large pressurized cylinders require vast amounts of time to assemble the interfaces between the cylinders and the micro-scale devices. The interface between the two systems normally requires steady hands, the use of magnification lenses, and micro-hole punches. Each interface must be configured manually, with each interface potentially critical to the functionality of the device. Additionally, the large pressurized cylinders often require compliance with stringent local and federal regulations to maintain the cylinders on the premises.
Referring to FIG. 1 an example of a microfluidic chip 100 which is interfaced with a large pressurized cylinder is shown. The microfluidic chip 100 includes a first reaction zone 102 and a second reaction zone 104. The first reaction zone 102 and the second reaction zone 104 perform similar functions and are typically redundant. The redundancy of the reaction zones 102 and 104 provide multiplexing capability. Each of the reaction zones 102 and 104 are fed from a number of feed lines 106, 108, and 110. The feed lines 106, 108, and 110 are embedded within the microfluidic chip 100 and transfer pressurized gas from external gas sources, such as cylinders, to the reaction zones 102 and 104. The feed lines 106, 108, and 110 are interfaced with the cylinders via connection tubes 112 and 114. Each of the connection tubes 112 and 114 require a substantial amount of time to interface with the micro-sized feed lines 106, 108, and 110.
As an alternative, chemical micro-pumps have been developed. The chemical micro-pumps produce pressure via chemical reactions to drive lab-on-chip processes. An example of such a pump was described by Yo Han Choi, Sang Uk Son, and Sueng S. Lee in “A micro-pump operating with chemically produced oxygen gas,” Sensors and Actuators, Vol. 111, Issue 1, March 2004, pages 8-13. The chemical micro-pumps use chemical reagents which are separated within the pump by a removable barrier. A wide of variety of chemicals have been proposed that will release a gas byproduct when mixed. The release of a gas is typically induced via a chemical reaction. In a closed or pressurized system, as the gas byproduct is released into a fixed volume, the magnitude of the pressure within the system increases.
The barrier is typically removed by applying heat and melting the barrier. Once the barrier is removed, the chemical reaction is initiated and takes place until the reagents are used up.
The pumping action of these devices is proportional to the amount of reagent available within the reaction chambers. Therefore, the reaction is wholly dependent upon the quantity of the reagents and can not be controlled once the reaction is initiated. The inconsistent availability of the reagents over time results in wide fluctuations in gas production. Similarly, the produced gas typically can not be sped up, slowed down, stopped, or varied. Although the chemical micro-pumps are inexpensive to fabricate, they are not reusable and therefore require a substantial amount of tooling time each time the pumps are exchanged.
As described above, existing methods fail to provide a portable and reusable device suitable for driving lab-on-chip processes. Therefore, a continuing need exists for an inexpensive and fully integrateable device for driving lab-on-chip processes. A further need exists for a device which can provide a constant pressure throughout the operation of the device. A still further need exists for a device which can produce a broad spectrum of pressures at a single time for distribution and which is controllable once the pressure generation system is initiated.